The present invention relates to the high intensity discharge (HID) lamp arts. It finds particular application in conjunction with ceramic metal halide discharge lamps and will be described with particular reference thereto. However, it should be appreciated that the present invention will also find application in conjunction with other types of high intensity discharge lamps and other applications which require precise control over setting arc gap lengths in a manufacturing environment.
High intensity discharge lamps operate by discharging an intense electrical arc between two electrodes. Ceramic metal halide discharge lamps typically include a ceramic arc tube mounted within an outer bulb. The ceramic arc tube includes a ceramic body having an electrode assembly sealed in each end thereof. One of the key advantages of ceramic metal halide discharge lamps is that they can provide good color uniformity. Achieving good color uniformity requires good control over arc tube voltage, which in turn is strongly dependent on the length of the arc gap, or the distance between the electrode tips.
During manufacture, the electrode assemblies are pushed into the ceramic arc tube body until crimps associated with each electrode assembly rest against the respective ends of the arc tube body. Each electrode tip position relative to an end of the arc tube body is determined by the distance from the electrode tip to the crimp. Thus, the length of the arc gap is equal to the overall length of the arc tube body less the sum of the two crimp lengths (i.e., the distance from the electrode tips to the respective crimps). With current production processes, the variation in overall arc tube body length is too great to permit adequate control of the arc gap length, and hence the arc tube voltage.
Accordingly, it has been considered desirable to develop a new and improved crimp length gauge for use with ceramic metal halide discharge lamps which meets the above-stated needs and overcomes the foregoing difficulties and others while providing better and more advantageous results.